1. Field of Invention
The present invention relates to current sensing; and more particularly, to a method and apparatus for sensing electrical current in a conductor.
Although the present invention is subject to a wide range of applications, it is especially suited for use in sensing the current in conventional or electric vehicles, and will be particularly described in that connection.
2. Discussion of Related Art lo Presently, for certain applications, Hall Effect devices are used to measure the DC current in conductors. These devices develop a DC voltage due to a DC current in a current carrying conductor placed in a magnetic field. The conductor is positioned so that the magnetic field is perpendicular to the direction of current flow and the electric field that creates the DC voltage is perpendicular to both. However, Hall effect sensors are costly and exhibit non-linearity over extreme temperature ranges.
Also, for certain applications involving high current, such as automotive battery and alternator cables, a precision low resistance is placed in series with the conductor. This resistance provides a voltage drop proportional to the conductor current that can then be used as an input to an engine control computer for power train optimization. A disadvantage is that the cable must be broken to insert the low resistance, resulting in a special assembly and potential long-term connection reliability problems. Additionally, this arrangement is not electrically isolated from the primary circuit and is prone to noise problems.
In light of the foregoing, particularly for sensing DC current in conductors, such as battery or alternator cables of motor vehicles, there is a need for a low cost, easily installed, reliable current sensing device that does not require a special cable assembly, is isolated from the primary electrical system, and is linear over a wide range of temperatures.